The present invention relates to devices for transporting sheets in or between printers, and more particularly to sheet handlers, feeders, and sheet transport mechanisms which are built into or added onto systems composed of one or more printers. It particularly relates to two-sided printing systems.
Among prior art printing or copying systems, it is common to provide, at the output of one print "engine" a transport mechanism to carry sheets that have been printed on one side, and to function as a collating, inverting or other specialized sheet handling system. U.S. Pat. No. 4,879,571 issued to one of the present inventors, Paul Plasschaert, shows one such specialized sheet handling system wherein an entering sheet from the output of one print engine is inverted side-to-side as it undergoes a right angle change in transport direction.
The inverting system described in that patent operates by driving a front corner of the moving sheet against a J-bar that extends into the paper path to initiate a curling-over of the corner. As the sheet continues to advance along the transport path, the curled-over edge pushes against an obstruction oriented at 45.degree. across the transport path, which causes the leading end to continue curling over as it makes a right angle turn into the output path. That transport allows the injection of half-printed (e.g., single-side printed) sheets from a side station, into a main printing line with the sheets flipped over for receiving a second print image, thus offering greater flexibility in configuring multi-printer systems.
It would also be desirable to flip a printed sheet without changing its transport direction, and preferably to do so in a short transport path.